In a line photographing process for a photographic plate making, an original typically is made by applying a phototypesetting character, a hand written character, an illustration, or a halftone-dotted photograph. This original is photographed with a plate making camera. The plate making camera is so designed that the exposure is controlled by the exposing time, and a photographic material having a higher sensitivity can be subjected to photographing in a shorter time. The shortening of delivery dates is required in the printing industry and this requires a photographic material having a higher sensitivity.
In the plate making field, a photographic material having a high contrast and a method for preparing it are required and various attempts therefor have so far been made. There have been developed the methods having a developing effect, such as a method in which a silver halide photographic material is processed in a developing solution having a very low sulfite ion concentration (a so-called lithographic developing system) and a method in which a silver halide photographic material containing a hydrazine derivative is processed in a developing solution having a high pH. In addition thereto, a method in which a rhodium salt is doped in the silver halide grains has been applied as a contrast increasing method in which the developing effect is not used.
As described above, high sensitivity and high contrast have been required in the plate making field. In recent years, simplification of processing methods and reduction of the amount of processing waste water have been required in addition thereto. This has required processes which maintain a high contrast even with a small replenishing amount.
The methods in which two or more silver halide emulsion layers are used and in addition, an image having a high contrast is formed are described in JP-A-51-50736 (the term "JP-A" as used herein means an unexamined published Japanese patent application), 62-235939, 62-90646, 62-150343, 63-15237, and 63-46437. In these methods, a high contrast is provided by the developing effect described above and the high contrast is not given by providing two or more silver halide emulsion layers.
An increase in the contrast by the provision itself of two or more silver halide emulsion layers each having a different sensitivity is described in JP-A-1-179145 but this method does not provide the high contrast required in the plate making field.